Help troubleshooting trunk electronics

[Pulelehua]

Working on troubleshooting parking distance sensors after buying an E53 with a really wet trunk - sunroof drain is repaired- and I'm trying to figure out -what the small module is & which module is missing (wiring harness on far right in picture).
I have a PDC module on the way from ebay.

[wpoll]

Small Siemens module is the towing module (AHM).

The spare harness may be for the air suspension module (EHC)?

[Pulelehua]

Thank you, that makes sense. I pulled apart each module apart, no apparent water damage. Each PDC Sensor makes clicking sounds when the button is pushed.... the front speaker is unplugged, as it came, worth plugging in now that I repaired the seat sensor with an override.